1. Field of the Invention
This invention relates to a prestroke controller for an engine fuel injection pump, more particularly to a prestroke controller for an engine fuel injection pump which during adjustment of an injection timing advance characteristic by use of one or more governor flyweights enables prestroke control independently of the flyweights or enables prestroke control altogether independently of flyweight lift and in addition transfers governor flyweight lift utilizing a magnetic coupling.
2. Prior Art
In some prior art fuel injection pumps the fuel injection timing advance characteristic is adjusted by controlling the prestroke. In the fuel injection pumps disclosed in Japanese Patent Disclosure No. Hei 3-233144 and Japanese Utility Model Application No. Hei 5-73755, for example, the prestroke is adjusted and the fuel injection timing is controlled by utilizing the movement (lift) of the governor flyweight(s) as a source of driving power for operating the timing control rod.
In a fuel injection pump equipped with a plunger which sucks in and pressurizes fuel by reciprocating axially, the prestroke refers to the stroke of the plunger between its bottom dead point and the point at which pressurized fuel delivery starts. The fuel injection characteristic appropriate for the engine operating condition is obtained by shortening the prestroke to cause the fuel injection to start earlier (injection timing advance) or lengthening it to cause the fuel injection to start later (injection timing retard).
The prestroke controller for a fuel injection pump taught by the aforesaid Japanese Patent Disclosure No. Hei 3-233144 will be briefly explained with reference to FIG. 39.
FIG. 39 is a perspective view of the prestroke controller for an engine fuel injection pump, designated by reference numeral 1, and a conventional mechanical governor, designated reference numeral 2. On the side of the main pump unit 3 are shown a plunger 4, a control sleeve 5, and a timing control rod 6 whose engagement pin 8 is engaged with an engagement groove 7 of the control sleeve 5.
On the side of the mechanical governor 2, a cam shaft 9 for reciprocating the plunger 4 in the main pump unit 3 is fitted with a guide sleeve 10 and a flyweight 11 is connected with the guide sleeve 10.
The prestroke controller for an engine fuel injection pump 1, which comprises the flyweight 11 as a component utilized in common with the mechanical governor 2, further has a tension lever 13 serving as a prestroke control lever which pivots around a stationary pivot shaft 12 in accordance with the movement of the flyweight 11, a timing cam 14, a counterweight 15 connected with the timing control rod 6, and a cam surface abutment piece 16 formed integrally with the counterweight 15.
The timing cam 14 is connected with one side of the free end of the tension lever 13 through a connection lever 17 and is rotatable around a stationary pivot shaft 18. A cam surface abutment projection 16A of the cam surface abutment piece 16 is pressed onto the cam surface 14A of the timing cam 14 at a prescribed pressure by the force of a counterweight spring 19 (return spring).
The other side of the free end of the tension lever 13 is connected with a torque cam 21 which is part of a governor mechanism 20 of the mechanical governor 2. Although this is for enabling the governor mechanism 20 to automatically control the fuel injection quantity in response to variation in engine load, the governor mechanism 20 will not be described in detail here.
An injection quantity control rack 22 is provided in association with the torque cam 21. The injection quantity control rack 22 controls the fuel injection quantity by rotating the plunger 4 about its own axis.
In the prestroke controller for an engine fuel injection pump 1 of the aforesaid configuration, an increase in engine speed (pump speed) increases the centrifugal force of the flyweight 11 causing it to shift and slide the guide sleeve 10 along the cam shaft 9 to the right in FIG. 39. As a result, the tension lever 13 rotates about the stationary pivot shaft 12, whereby the mechanical governor 2 performs the prescribed governor function and the timing cam 14 is rotated about the stationary pivot shaft 18 by the connection lever 17.
Since this rotation of the timing cam 14 changes the positional relationship between the timing control cam surface 14A and the cam surface abutment projection 16A of the cam surface abutment piece 16, the cam surface abutment piece 16 and the counterweight 15 are rotated about the axis of the timing control rod 6.
The resulting rotation of the timing control rod 6 by a corresponding angle moves the control sleeve 5 vertically and changes the positional relationship between the control sleeve 5 and the plunger 4, thus changing the fuel injection timing or the prestroke.
As explained in the foregoing, the prestroke controller 1 controls the start of pressurized fuel delivery by the main pump unit 3 by changing the position of the control sleeve 5 relative to the axial direction of the plunger 4. For this, the position of the control sleeve 5 is changed by operating the timing control rod 6.
In addition, the flyweight 11 and tension lever 13, which are members of the governor mechanism 20, are employed for operating the timing control rod 6 to change the position of the control sleeve 5.
Since the flyweight 11 utilized by the prior art prestroke controller 1 moves with increasing engine speed, the prestroke controller 1 is incapable of providing the injection timing advance characteristic required of a speed timer for varying the injection timing as a function of engine speed. The prior art prestroke controller 1 thus has the drawback of being all but impossible to apply for controlling prestroke in accordance with an injection timing advance characteristic during operation in a cold external environment or in response to changes in the amount of accelerator depression or the engine load state.
FIG. 40 is an enlarged sectional view of an essential portion of the coupling (displacement transfer section 23) between a mechanical governor 2 and a main pump unit 3 of the fuel injection pump of the aforesaid Japanese Utility Model Application No. Hei 5-73755. A displacement transfer rod 24 connected with a flyweight 11 (not shown) through a tension lever 13 (not shown) and the like transfers displacement to a timing control rod 6 through a partition 25 by means of a magnetic coupling 26.
The magnetic coupling 26 includes a driving side external magnet 27 and a driven side internal magnet 28. By rotating the displacement transfer rod 24 a rotational force can be transferred to the timing control rod 6 through the magnetic coupling 26.
The various merits obtained by utilizing the magnetic coupling 26 of the aforesaid configuration for the transfer of torque include: that the structure can be made simpler and more reliable than in the case of the conventional mechanical governor 2 requiring a fuel seal, that low temperature operation is made possible, that the injection quantity control function of the mechanical governor 2 is not lost even if the control sleeve 5 should stick for some reason, that forces produced by external disturbances can be canceled by the counterweight 15 (FIG. 39), and that the absence of contact with the controlled member (the timing control rod 6) ensures that the injection quantity control function of the mechanical governor 2 is not affected during idling.
Moreover, as can be seen in FIG. 41 showing the magnetic coupling 26 as viewed from the side of the mechanical governor 2 toward the main pump unit 3, a self-aligning torque T arises when the driving side external magnet 27 and the driven side internal magnet 28 are offset from their neutral state by an angle .theta.. The characteristics of the self-aligning torque T are shown in FIG. 42.
When the magnetic coupling 26 is utilized for torque transfer, it is able to transfer the peak value of the self-aligning torque.
The magnetic force of a magnetic such as the driving side external magnet 27 or the driven side internal magnet 28 varies with temperature. For example, a ferrite magnet demagnetizes at low temperatures while a neodymium magnet demagnetizes at a high temperature. Because of this, the displacement of the driven side internal magnet 28 on the output side produced by a given displacement of the driving side external magnet 38 on the input side decreases by an angle proportional to the load torque (approximately equal to the force which the counterweight spring 19 (FIG. 39) applies to the timing control rod 6) at each of angles .theta..sub.1, .theta..sub.2, .theta..sub.3.
Thus when torque is transferred by angular displacement in this way, a deviation proportional to the self-aligning torque T occurs in the angle .theta..
This gives rise to the problem that the minimum prestroke position (maximum injection timing advance position) varies with the ambient temperature.
In other words, as shown in FIG. 43, owing to the temperature dependency of the driving side external magnet 27 and the driven side internal magnet 28, the amount of timing advance (prestroke) for a given pump speed Np, specifically the minimum prestroke, is not constant, creating the problem that the amount of timing advance is destabilized by the ambient temperature.
When torque is transferred from the side of the mechanical governor 2 to the side of the main pump unit 3 using the magnetic coupling 26, it is conceivable to control the prestroke characteristic by inserting a component such as a cylindrical cam with a prescribed cam surface. It is, however, necessary to provide a mechanism that exhibits a sufficient torque transfer capability and that does not adversely affect the operation of the injection quantity control rack.
Moreover, when the prestroke is controlled in accordance with movement of the flyweight 11, it is necessary to be able to adjust the prestroke control start time.
As was explained in the foregoing, the magnetic coupling 26 serves as a safety mechanism ensuring operation of the tension lever 13 side, namely the function of the governor mechanism 20 as a control mechanism for the injection quantity control rack 22, even if sticking should occur on the side of the timing control rod 6 for some reason. If the magnetic coupling 26 should stick for some reason, however, the tension lever 13 will be immobilized, making it impossible for the mechanical governor 2 (the governor mechanism 20) to fulfill its control function.
More specifically, since disablement of the tension lever 13 makes control of the fuel injection quantity by the mechanical governor 2 impossible, overrun or some other such major problem may arise. It is therefore important to provide some kind of safety mechanism for the magnetic coupling 26 itself.
In addition, it is sometimes necessary to be able to control the prestroke altogether independently of the movement (lift) of the flyweight 11.
An object of the first aspect of the invention is to overcome the aforesaid problems of the prior art technology by providing a prestroke controller for an engine fuel injection pump which utilizes a magnetic coupling and which, by taking advantage of the fact that the secondary side (driven side internal magnet) of the magnetic coupling can be controlled to a desired position without being driven by force from a flyweight on the primary side (driving side external magnet), not only secures speed timer characteristics but also, by establishing a greater degree of freedom in determining the injection timing advance characteristic, enables injection timing advance in response to temperature or load.
Another object of the first aspect of the invention is to provide a prestroke controller for an engine fuel injection pump enabling low-temperature injection timing advance and low-load injection timing advance independently of engine speed (flyweight lift).
An object of the second aspect of the invention is to provide a prestroke controller for an engine fuel injection pump which capitalizes on the advantages of utilizing a magnetic coupling and further prevents change in minimum prestroke position owing to change in ambient air temperature.
An object of the third aspect of the invention is to provide a fuel prestroke controller for an engine fuel injection pump which, in the case where torque is transferred from the side of a mechanical governor to the side of a main pump unit using one or more flyweights and a magnetic coupling, achieves efficient torque transfer capability by efficiently driving the magnetic coupling for controlling the prestroke characteristic.
An object of the fourth aspect of the invention is to provide a prestroke controller for an engine fuel injection pump which, in the case where one or more flyweights and a magnetic coupling are used and prestroke is controlled in accordance with flyweight lift, also enables adjustment of the prestroke control start time thereby enabling both adjustment of the prestroke control characteristic and matching adjustment.
An object of the fifth aspect of the invention is to provide a prestroke controller for an engine fuel injection pump which, in the case where the lift of one or more flyweights of a mechanical governor is transferred as displacement by a magnetic coupling, is capable of ensuring operation of the mechanical governor even if the magnetic coupling should stick.
Another object of the fifth aspect of the invention is to provide a prestroke controller for an engine fuel injection pump provided with a safety mechanism for enabling operation of a tension lever of the governor mechanism even if the magnetic coupling should stick.
An object of the sixth aspect of the invention is to provide a prestroke controller for an engine fuel injection pump which enables prestroke control in response to the degree of depression of an accelerator pedal altogether independently of flyweight lift.